Colloid mill and method of operating the same



Jan. 15, 1935. H, R RAFTQN coLLoID MILLV AND METHOD 0F OPERATING THESAME n .Il

Filed June 7, 195o #moLoQQArra/y Patented 15, 1935 UNITED STATES PATENTOFFICE Harold Robert Rafton, Andover, Mass., assigner to Raffold ProcessCorporation, a corporation of Massachusetts Application June 7, 1930,Serial No. 459,816

9 claims.

This invention relates vto an improved colloid mill and method ofoperating the same.

Colloid mills, which are machines for reducing materials to a very finestate of subdivision, are of several types, but the present inventionconcerns the type of mill wherein a material in liquid suspension ispassed through a gap of definite and controllable size, formed by thecooperating surfaces of two substantially rigid or non-exible elements,at least one of which is rotatable at high speeds. The present inventionalso is applicable to colloid mills wherein bothof the elements aremovable, such movement usually being imparted by rotat-ing the elementsin opposite directions.

The gap existing between the cooperating surfaces of the elementsusually is controllable as to size by a micrometer screw adjustment. Thetwo cooperating surfaces which define the gap through whichnthe materialin liquid suspension passes. may be of the smoot-h type. vor either orboth surfaces may have depressions or projections Aof various designsthereon, provided such depressions or projections are not of such anature as to interlock and prevent rotation if the surfaces be broughttogether..

The cooperating .surfaces may be of any desired shape. For example.these .surfaces may be of a fiat disc or annular shape. or they may bemore or less conical or frustro-conical. orsections of a sphere onefitting within the other so that by movement such as coaxial movement)of one within the other the surfaces may be brought more closelytogether.

Mills of the type referred to with substantially smooth cooperatingsurfaces are supposed to subdivide materials by a shearing action whichtakes place within the liquid lm between the two cooperating surfaces.and not by any grinding action. In cases where the cooperating surfacesare not smooth. the mills are supposed to have. in addition to the lmshearing action, a cutting or impacting action.

When substantially immiscible liquids have been run through colloidmills of the adjustable gap substantially rigid element type abovedescribed. fine dispersions of the liquids one in the other have beenobtained in some cases. but where solids in liquid suspension have beenrun through such mills. the results as to particle subdivision, in manycases have been disappointing. Colloid mills of this type are notsuitable for reducing the particle size of extremely finely dividedsolids,

and even with relatively coarse particle size solids the results havebeen poor. This is particularly true where the material .originallycontained only a relatively small proportion of oversize material, whichmay be considered as particles larger than .001".

An important object of the present invention is to provide a novelmethod of operating a colloid I mill to provide more satisfactoryresults as to the reduction of oversize particles.

A further object is to provide a method of operating a colloid mill bysubjecting the material to the action of the cooperating surfaces whilesubjecting the latter to a yieldable pressure tending to move themtoward each other.

A further object is to provide a. colloid mill f which is adapted toproduce a more satisfactorily subdivided material when materials ofrelatively coarse particle size are to be treated.

A further object is to provide a colloid mill wherein the improvedresults referred to are obtained by subjecting the cooperating `surfacesto yieldable pressure tending to move them toward each other while thematerial being acted upon passes between such surfaces.

Other objects and advantages of the invention will become apparentduring the course of the following description.

As stated above, the usual adiustable gap substantially rigid elementtype colloid mills rely for their operation on the transmission of ashearing action to the lm between the cooperating surfaces and/ or animpacting action inherent in the operation of the mills when thecooperating surfaces thereof are arranged with a xed gap therebetween. Ihave found that instead of relying upon the actions referred to, agrinding action may be inducedby bringing the cooperating sur- 35 facesof the rigid elements sufficiently close together, and maintaining thisrelationship by pressure. The degree of reduction of particle sizeobtainable under such conditions with material of relatively coarseparticle size is greatly lmproved. and the reduction of oversizeparticles in materials containing a relatively small proportion thereofcan be successfully carried out. However, stoppage of the mill withfrequent consequent damage theretoresults if the gap between thecooperating surfaces is reduced to nearly zero by non-yielding pressureduring the operation of a high speed mill.

I have found that this difficulty can be overcome if the cooperatingsurfaces be brought substantially together by a yieldable pressureduring the operation of the mill. 'I'he gap between the surfaces by thisexpedient can be reduced to an almost negligible size, if desired,without interfer- 55 ing with the operation of the mill or causingdamage thereto.

In the practice of my invention, I apply pressure yieldably through theagency of one or both of the substantially rigid element or elements tothe cooperating surfaces thereof. Such yieldable pressure may be appliedin several ways. For example, a spring may be mounted in such a mannerthat pressure applied thereto will bring the two substantially rigidelements yieldably together. The desired results similarly may beaccomplished by the application of hydraulic pressure, by theapplication of a Weighted lever system, or by the application of theyieldable pressure electrically. As an example of the latter method, oneor both of the cooperating elements may be magnetized in such a Way asto tend to bring the cooperating surfaces thereof together, or thisresult may be accomplished by using a solenoid acting on the shaft ofone of the elements. Other methods will occur to one skilled in the art.In order to illustrate my invention, its application has been shown to acolloid mill in which the element bearing one of the cooperatingsurfaces is stationary, and may be called a stator and in which theelement bearing the other cooperating surface is rotatable at highspeed, and may be called a rotor. Such a mill is of the type illustratedin the patent to F. J. E. China, No. 1,523,632, which is commerciallyavailable and in more or less common use. It is to be understood,however, that the invention is equally applicable to other colloid millsof the adjustable gap substantially rigid element type described above.

As stated above, the present method contemplates the application ofyieldable pressure to one or both of the cooperating surfaces to tend tomove them toward each other. More specifically, the method contemplatesthe initial operation of the mill Without the application of suchyieldable pressure, the feeding of the material to the mill, and thesubsequent application of the desired yieldable pressure tending to movethe cooperating surfaces toward each other to effect a combinationmilling action, which includes the subjection of the material to agrinding action whereby greatly improved results are obtained.

In the drawing I have shown one organization 'of apparatus elementsadapted for practicing the invention. In this showing,

Figure 1 is a central vertical sectional view showing the parts in theinitial operating position, and,

Figure 2 is a similar view showing the parts substantially in the fullyoperative position.

The illustrated embodiment of the invention includes a preferably castmain body 10 having inlet and outlet ducts 11 and 12 respectively. 'Iheduct 11 is adapted for connection at its outer end to a suitable sourceof raw material supply and communicates at its inner end with a verticalduct 13 closed at its lower end by a plug 14.

The upper end of the duct or passage 13 communicates with a basin 15from which the material is fed upwardly past the frustro-conicaltreating face 16. As previously stated, the embodiment of the inventionillustrated is of the type which includes stationary and rotatingcooperating faces, and accordingly the face 16 may be considered asforming a part of a stator 17. After passing the stator, the treatedmaterial flows over into a receiving chamber 18, the lower face of whichis inclined downwardly as at 19 toward the Outlet duct 12.

The body 10 is provided at the lower end thereof with an outstandingannular ange 20 having openings 21 therethrough. These openings are forthe reception of bolts for securing the device to a suitable supportingsurface. The upper end of the body 10 also is provided with anoutstanding annular flange 22 for a purpose to be described.

The receiving chamber 18 is closed by a preferably cast cover 23 havinga peripheral flange 24 seating upon the flange 22. Bolts 25 pass throughsuitable openings in the anges 22 and 24 for securing the body 10 andcover 23 to each other. Access to the chamber 18 may be had through anopening 26 normally closed by a suitable plug 27.

A support indicated as a whole bythe numeral 28 is arranged over thecover 23. This support includes a bottom plate 29 seating against thetop of an upstanding flange 30 formed integral with the cover 23. Thesupport may be secured in the position illustrated by any suitable means(not shown). The plate 29 is provided with a central depending sleeve 31fora purpose to be described.

A rotor shaft 32 extends upwardly through the plate 29 and sleeve 3l.'Ihis shaft carries a rotor 33 at its lower end, provided with afrustro-conical face corresponding to and arranged concentric with theface 16, in close proximity thereto.

The rotor shaft is mounted to rotate in a bearing 34 which may be of astandard type including a plurality of anti-friction balls running ininner and outer races as shown. The inner race of the bearing rests uponan annular shoulder 35 formed on the shaft 32. Packing 36 is arrangedwithin the bottom of the sleeve 3l to minimize the leakage of lubricantdownwardly along the shaft, and the packing is held in position by a.retainer 37. Any lubricant leaking downwardly beyond the packing 36 isintercepted by a throw-ofi flange 38. When the shaft is rotating at ahigh speed, the centrifugal force developed by the flange 38 is adaptedto throw any lubricant intercepted thereby outwardly to the adjacent topface of the cover 23.

'I'he support 28 includes a tapering body 39 which is open at one sideas at 40. The body of the support carries a split internally threadedsleeve 41 at its upper end, and the split ends 42 of the sleeve areadapted to be drawn toward each other by a suitable clamping bolt 43. Amicrometer head 44 is threaded in the sleeve 41 and is adapted to beretained in adjusted positions therein by operating the clamping bolt43. A peripheral flange 45 is carried by the head 44 above thesleeve 41and is adapted to be engaged by a spanner wrench or other suitable toolto permit rotation of the head 44.

The upper end of the shaft 32 extends through a bearing 46 mounted inthe head 44. This bearing also may be of a standard type including aplurality of anti-friction balls running in inner and outer races. 'Ihebearing 46 preferably is of a type adapted to operate as a thrustbearing, but if the rotor is intended to be subjected to very heavy endthrust, it is advisable that a bearing of the usual type for thrustalone be suitably employed adjacent the top of the shaft 32, preferablyin addition to bearing 46.

The inner race of the bearing 46 contacts at its upper end with thelower of a pair of lock nuts 47 when the parts are in the positionsillustrated in Figure 1. The outer race of the bearing 46 is supportedat its lower` end by the head 44 and contacts at its upper end with a,portion of a cover i surrounding the shaft 32.

, shaft 32, as indicated atV thence to the pulley 53 48 secured to thetop of the micrometer head 44. Accordingly it will be apparent that theouter race of the upper bearing is positively fixed with respect to thehead 44.

It will be apparent that the inner race of the upper bearing does notseat upon the head 44, the latter being provided with a small recess 49.The lower end of t-he inner race of the bearing 46 contacts with a.vertically movable sleeve 50 The lower end of this sleeve contacts withthe upper end of a compression spring 51 mounted in an annular recess 52formed in a pulley 53 through which power is delivered to the device.The pulley is keyed to the 54. The belt for the pulley is adapted toextend through the open side 40 of the body of the support 28.

The lower end of the pulley 53 contacts with the upper end of the sleeve55, and the lower end of this sleeve contacts with the upper end of theinner race of the bearing 34. The sleeven55 extends through a coverplate 56 arranged on the upper end of the sleeve 31 and is held inposition thereon by screws 57 or similar fastening elements.

The operation of the device is as follows:

When the micrometer head 44 is raised so that there is a relativelylarge gap between the cooperating faces of the stator 17 and rotor 33,as shown in Figure 1, the spring 51 is uncompressed so that the bottomof the compression sleeve 50 is level with the top of the pulley 53. andthe locl; nuts 47 are in contact with the upper end of the inner race ofthe bearing 46. The parts are arranged in t-he positions described whenit is desired to start the operation of the device. Under suchconditions, the material to be treated is supplied from the source undersuitable pressure, to the duct 11 from whence it flows into the duct 13and basin 15. and thence upwardly between the cooperating faces of thestator 17 and rotor 33. The operation of the rotor, of course, will havebeen started at such time. and the speed of rotation will be determinedin accordance with the desired results sought to be obtained.

rThe gap between the cooperating faces. as illustrated in Figure 1. issomewhat exaggerated. but it will be apparent that this gap is somewhatgreater when the operation of the machine is initiated'than after theparts have been placed in the fully operative positions to be described.This being the case, the material flowing from the treating surfaceswill be incompletely treated. This material flows over into the chamber18 and thence drains downwardly to the outlet duct 12. and the initiallyincompletely treated material preferably is returned to the source forretreatment.

After the device has been placed in operation in the manner described.the bolt 43 is loosened and the micrometer head is turned downwardly.This movement is transmitted through the upper bearing 46 to thecompression sleeve 50. and through the spring 51. Owing to therelatively large gap initially provided between the coacting faces ofthe mill. the spring 51 will not be compressed. and accordingly thepulley will' move downwardly' to transmit movement to the shaft 32 andto the rotor 33. thus bringing the conical face thereof into closeproximity to the face 16. Under such conditions. the rotor 33 willoccupy substantially the position shown in Figure 2. while the sleeve 50and pulley 53 will still occupy substantially the relative positionsshown in Figure 1. In this connection it will be noted that thecooperating faces have been illustrated in Figure 2 as being in contactwith each other. Actual contact however never takes place under thecorrect conditions of operation, the film of material between the twofaces preventing such contact. However, the surfaces are brought veryclose together, to an almost negligible gap if desired, and in thismanner the grinding is accomplished.

Actual operation takes place with the rotor exerting substantialpressure downwardly against the film of material passing between thecooperating faces. Accordingly the micrometer head is turned downwardlybeyond the point described without causing substantially any furtheractual axial movement of the rotor, and accordingly the small gapreferred to between the cooperating faces is retained. Under suchconditions, however, the spring will be compressed as shown in Figure 2,the lower end of the sleeve 50 moving .downwardly fora short distanceinto the lannular recess 52. Accordingly actual operation is carried outwith a substantial pressure exerted on the film of material, and whenthe'device is properly operated under the condition referred to, thatis, with proper spring tension exerted downwardly on the rotor, thelatter will not seize with respect to the stator, and thus damage to thedevice is prevented. At the same time, the application of such resilientpressure provides far more eicient results than can be obtained with theusual relative movement between cooperating faces formed on inherentlyrigid members which are arranged to provide a fixed gap between theoperating faces.

Should the film between the rotor and stator be broken down, as byshutting off the supply of material, or by screwing down the micrometerhead beyond the compressive limit of the spring, it is apparent thatseizing will take place with the consequent chance of injury to themill. Thus care must be taken to prevent the occurrence of either ofthese conditions.

Instead of the screw micrometer device. the bearing 46 may be held in asimilar suitable holder sliding in the sleeve 4l (which in this casewould not be threaded) and the pressure applied to such device by alever or toggle joint (not shown) instead of by a screw. In such casethe mill may be fitted' with a suitable mechanical or electrical deviceto release the pressure automatically in case of a failure of supply.

The illustrative example of my invention shows a belt driven mill. Ofcourse, a direct motor or turbine drive may be employed instead of abelt, in which case however there should preferably be a flexiblecoupling connecting the shaft of the motor orl turbine with the shaft ofthe rotor which coupling should provide for suicient longitudinal motionto permit the operation of the pressure applying device.

It will be apparent that a spring of any desired compressive strengthmay be employed. Although it is understood that I do not limit myself inany way to springs of any particular strength. I have found it feasibleto employ springs of a wide range, e. g. of 40 to 1.000 lbs. compressivestrength in a mill employing a 5 inch rotor. In general. I have foundthat springs with higher compressibility give better results. In thisconnection it will be noted that the spring can be mounted in anydesired manner so long as it acts to allow pressure to be yieldablyapplied. It also will be apparent that the rotor may be mounted rigidlyagainst longitudinal movement `and that the spring pressure may beapplied to are employed, in which is further applicable to types ofmills other than those illustrated and referred to, for example toso-called paste mills which are cclloid mills adapted for treatingrelatively concentrated suspensions or semi-solid pastes.

The feed may be supplied to the mill under any pressure desiredaccording to the design of the mill and the spring pressure employed,but in actual operation of the mill illustrated. I have found that apressure corresponding to that of a head of liquid of a few feet from afeed tank is sufficient. With paste mills pressure feed is preferable.

As previously stated, it is desirable that the portion of thematerialpassing through the mill at the initiation of the operationthereof should be by-passed to the original feed tank until the mill hasbeen adjusted to the position shown in Figure 2. This likewise appliesto the material passing through the mill just at the end of the run. Inthis connection, it is noted that when it is desired to shut down theoperation of the mill, the spring pressure is released before cuttingoff the supply of material to prevent seizure between the cooperatingsurfaces.

The invention upon solids in apparatus.

The invention obviously is not limited to any definite relative rotativespeeds between the cooperating surfaces. For example, the millillustrated has been operated from 3,200 to 14,000 R. P. M., but I havefound in general that bet-ter results are obtainable at higher rotativespeeds.

win be obvious that forthe same peripheral speed rotors of largediameter operate at lower shaft speeds.

In certain cases, the desired results may not be obtained by one passageof the material through the mill. In such cases the material may begiven more than one passage through the mill, or in some cases, part ofthe eiliuent may be bypassed to the inlet side of the apparatus so as toobtain continuous operation.

The rotor and stator have been illustrated as mill. that the cooperatingsurfaces be made detachable and thus renewable when worn.

The advantages of the apparatus will be apparent from the foregoingdescription. The in- With a substantial gap therebetween, initiating acontinuous feed of material between the cooperating faces, and thenmoving the cooperating faces toward each other and maintaining them inclose proximity under the influence of yieldable force. The practice ofthe method obviously provides the desirable efficient results referredto above.

While I have described in detail one embodiment of my invention, it isto be understool that I do not intend to be limited thereby, as it isapparent that various changes may be made in the device and in theprocedure of the method without departing from the spirit of theinvention or the scope of the subjoined claims.

I claim:

of a liquid suspension of such solids through a 1 passage of materialtherebetween.

4. In a colloid mill comprising a pair of relatively rotatablerespectively rigid elements having yieldable pressure means and thenmovable further in the same direction in engagement with said rst namedelement for positively moving the second named element.

ward said second named element to tend to hold said4 surfaces incooperative relationship, and means contacting with said yieldablepressure means and movable in one direction to increase the forcethereof tending to move said first named element toward said secondnamed element, said last named means being movable initially in theother direction for releasing said yieldable pressure means and thenmovableY further in the same direction in engagement with said firstnamed element for positively moving the latter away from the secondnamed element.

6. In a colloid mill comprising a pair of respectively rigid elementshaving cooperating material treating surfaces, that improvement whichconsists in mounting one of said elements for unrestricted movementtoward the other element, a spring compressible in contact with saidfirst named element to tend to move it axially toward said second namedelement to hold said surfaces in cooperative relationship, and meanscontacting with said spring and movable in one direction to increase thedegree of compression thereof, said last named means being movableinitially in the other direction for releasing the compression of saidspring and then movable further in the same direction in engagement withsaid first named element for positively moving the latter away from thesecond named element.

'7. In a colloid mill comprising a pair of respectively rigid elementshaving cooperating material treating surfaces, that improvement whichconsists in mounting one of said elements for unrestricted movementtoward the other element, at least one of said elements being rotatableat high speeds, means for rotating said last mentioned element, a springcompressible in contact with said rst named element to tend to move itaxially toward said second named element to hold said surfaces incooperative relationship, and means contacting with said spring andmovable in one direction to increase the degree of compression thereof,said last named means being movable initially in the other direction forreleasing the compression of said spring and then movable further in thesame direction in engagement with said first named element forpositively moving the latter away from the second named element.

8. A colloid mill comprising a rotor and a stator having cooperatingsurfaces, said rotor being slidably mounted for movement toward saidstator to bring said cooperating surfaces into yclose proximity,yieldable pressure means acting on said rotor for maintaining saidcooperating surfaces in close proximity, and means contacting with saidyieldable pressure means and movable in one direction for increasing theactive pressure thereof against said rotor, said last named means beingmovable initially in the other direction for releasing said yieldablepressure means and then movable further in the same direction in Contactwith said rotor for positively moving the latter away from the stator.

9. A colloid mill comprising a rotor and a stator having cooperatingsurfaces, said rotor being slidable axially to bring said cooperatingsurfaces into close proximity, a compression spring acting on said rotoraxially thereof for maintaining said cooperating surfaces in closeproximity, and

means contacting .with said compression springv and movable in onedirection for compressing the latter. said last named means beingmovable initially in the other direction for releasing the tension ofsaid spring and then movable further in the same direction in contactwith said rotor for positively moving the latter axially away from thestator.

HAROLD ROBERT RAFTON.

